Progesterone and pregnenolone sulfate in pregnancy plasma

Abstract

The role of adrenocortical precursors in placental progesterone production in normal pregnancy has been investigated by measuring plasma steroid levels in blood samples obtained concomitantly from various vascular regions, maternal and fetal, in 28 women at the moment of delivery. Pregnenolone sulfate level was found in the highest concentration 170.0 μg per cent ± 26.5 in the umbilical artery supplying the placenta, significantly higher than in the umbilical vein draining this organ (124.0 μg per cent ± 17.7). Inversely, progesterone concentration was higher in the fetal umbilical vein 96.6 μg per cent ± 8.8 than in the artery 53.6 μg per cent ± 5.5. The highest progesterone level 133.9 μg per cent ± 12.4 and a very low pregnenolone sulfate level 37.1 μg per cent ± 5.3 were found in blood samples from the intervillous space. The lowest plasma levels of both steroids have been found in maternal venous blood: progesterone 12.5 μg per cent ± 1.2 and pregnenolone sulfate 27.8 μg per cent ± 3.5. Increasing markedly maternal plasma pregnenolone sulfate by intravenous infusion of this steroid or decreasing it by dexamethasone adrenal suppression did not affect maternal plasma progesterone level. It is concluded that pregnenolone sulfate of adrenal origin does not seem to act as a progesterone precursor to any significant extent.